This invention relates to tunnel reinforcements.
The word tunnel is used in this specification to encompass any apertured structures, such as an arched bridge, of any length. But other remedies can often be applied to short structures such as bridges where there is access to the outside of the arch.
Tunnels are often lined, and old ones are usually brick-lined. While many have survived remarkably well for over a hundred years or more, they do inevitably deteriorate and require attention. Sometimes, just re-pointing and the replacement of some bricks is sufficient, but when there has been movement and the original lining is distorted, or is reckoned to be at risk of collapse, more drastic treatment is required.
One method is to re-line the tunnel, covering the old brickwork with concrete. This is expensive, uses a great deal of material, and inevitably reduced the tunnel bore. Also, it does not lend itself to very local reinforcement, which may be all that is required.
A problem with tunnel linings is that they are only accessible from inside, and their curvature has usually meant that reinforcing bolts into the surrounding strata have extended substantially normally to the lining. Of course, those are virtually useless in sand, earth or rubble; they need to go into rock.
It is the aim of this invention to enable tunnel linings to be reinforced within themselves, enabling ever local strengthening and being independent of the nature of the ground through which the tunnel extends.
According to the present invention there is provided a method of reinforcing tunnel linings comprising the steps of:
(i) cutting a groove into the lining from inside, the mouth of the groove being narrower than the remaining enlarged part of the groove,
(ii) injecting an embryo elongate reinforcement comprising at least one rod within a fabric sleeve through the mouth of the groove into said enlarged part, and
(iii) injecting grout to fill the sleeve and expand it against the surface of the enlarged part, the grout seeping through and bonding to the lining, thereby completing the reinforcement.
Conveniently the groove will be formed in stages:
(i) a substantially parallel sided groove being cut into the lining from inside,
(ii) a heading wider than the preliminary groove being made into that groove,
(iii) a rotary cutter head with a diameter wider than the preliminary groove being entered into the heading so that the cutter head is beyond the inner surface of the lining and so that a shaft carrying the head registers with the preliminary groove, and
(iv) the cutter head being rotated and traversed at substantially constant depth within the lining with the shaft being guided along the preliminary groove thereby to enlarge the preliminary groove internally of the lining.
Stages (i) and (ii) may be reversed.
One heading will generally be made at one end of the groove and a similar heading made at the other end, through which the cutter head may be withdrawn after the enlargement has been made.
The headings can be drilled deep, through the lining into surrounding rock, whereby each can received an elongate anchoring member that locks into the rock. The ends of the reinforcement are then advantageously captive to the elongate anchoring members within the headings.
These elongate anchoring members may be expansion bolts, or fabric sleeves containing one or more reinforcing rods, each sleeve being expanded and filled by grout injection. In another version, the embryo reinforcement may be longer than the groove and have its ends angled to extend out beyond the lining into the deep headings and to serve as the elongate anchoring members. A single grout injection then suffices to complete and make unitary the reinforcement and the anchoring members.
The reinforcement, when filled with grout, will often bulge into the mouth of the groove but not fill it. The filling can be completed by further grouting or pointing.
The reinforcement may have a plurality of generally parallel rods interconnected at intervals by spring elements that urge them apart. The rods can be bunched up to get thorough the narrow mouth of the groove, but then they will spread out again in the enlarged part.
The method will generally be repeated to form a set of reinforced grooves along a tunnel. These may follow the maximum curvature of the lining, or be skew thereto. Two sets of reinforced grooves may be provided, the enlarged parts of one set being deeper into the lining than the enlarged parts of the other set, and at least some of the grooves of one set being angled to cross at least some grooves of the other set. A reinforcing grid is thus formed.